This invention relates generally to combustion engines, and more particularly to increasing the safety and performance of engines used for marine applications.
Many types and models of engines are commercially available for integration into power systems for a variety of applications. One line of such engines is the DM700G/DM950G series available from BriggsandStratton-Daihatsu. For some applications, such as providing propulsion or secondary power generation on boats, particularly stringent safety requirements are demanded by law. In the case of marine engines, the performance of safety systems is specified in the United States by the U.S. Coast Guard. For example, 33 C.F.R. xc2xa7183.526 specifies a fuel leakage test for carburetors of marine engines. To pass such tests, commercially available engines are typically modified to run any carburetor bowl vent to the intake manifold to avoid leaking any liquid fuel such as, for example, when the throttle is opened with the carburetor float stuck.
In most applications, it is also desirable that engines perform with as little audible noise as possible. This is especially true for electrical power generation on boats, as such generator systems frequently operate in an absence of background noise.
Other desirable engine attributes include low emission of pollutants and high fuel efficiency.
The invention features several improvements in the design and structure of engines that, for example, improve their suitability for marine applications such as on board electrical power generation.
One such improvement is an intake silencer for use with side-draft carburetors. The intake silencer of the invention defines an internal volume sized to help attenuate air pressure fluctuations generated within the carburetor and engine and transmitted back through the entering combustion air, and also functions as a flame arrester to inhibit the propagation of sparks or flame from the carburetor to the surrounding atmosphere.
In some embodiments, the intake silencer also defines an internal drip well at the bottom of its internal volume to collect fuel droplets and condensing vapors during, for example, the carburetor leak test specified in 33 C.F.R. xc2xa7183.526. Preferably, these collected liquids are siphoned through a hose back to the engine intake system for combustion.
In the present embodiment, the intake silencer defines an attachment at one end for a tuned pipe or xe2x80x9czip tubexe2x80x9d, in hydraulic communication with the internal volume of the silencer, to provide a quarter-wavelength attenuator.
Another such improvement deals with carburetor bowl venting. Instead of suctioning carburetor bowl gasses into the intake manifold at negative gage pressure, as has been done in marine applications employing commercially available engines, in the improved engine the carburetor bowl is vented to the atmosphere through a check valve that operates to allow gas and relatively safe vapor out of the carburetor during venting, but disallows liquid fuel from flowing out of the carburetor through the vent. In early tests, this improvement was able to significantly reduce the emissions of the engine under some operating conditions, as compared with the same engine with the carburetor bowl vented into the carburetor inlet.
In another aspect, the invention features an air intake component, such as a silencer or air filter housing, adapted to be attached to a carburetor and including a check drain valve hydraulically connecting the component to the intake manifold of the engine. The drain valve enables liquid fuel to be sucked into the engine from the component but inhibits the transfer of air. In one embodiment the valve includes a check ball that normally seats against the inner surface of the drain to prevent the flow of air into the manifold under manifold vacuum pressure. The ball is constructed to float on liquid fuel, such that in the presence of a sufficient quantity of liquid fuel the ball will rise from its seat and permit the liquid fuel to be sucked into the manifold. This valve is particularly effective for use with engines equipped with side draft carburetors attached to intake components, upstream of the carburetor, with inner cavities that extend to a lower elevation than the carburetor inlet and can therefore tend to collect liquid fuel.
Another engine improvement features a damper applied to an engine speed control linkage to dampen linkage oscillation and improve engine speed stability. We have found that connecting the governor speed control lever of certain commercially available engines to the associated engine block with a dashpot can dampen the speed oscillations experienced during a rapid load change without significantly impairing engine speed response time. This improvement is particularly useful for engines coupled to electrical generators or otherwise intended to operate at a fairly constant speed for an extended period of time. For driving AC generators, engine speed stability is extremely necessary for maintaining generator frequency, as well as output voltage stability. We have found, for instance, that proper dashpot and spring selection can improve the suitability of Daihatsu DM700G/DM950G series engines for driving AC generators.
The details of one or more embodiments of these improvements are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.